1. Field
The present disclosure relates to plastic lenses and lens barrels.
2. Description of the Related Art
When a light beam is incident on an imaging optical system composed of a plurality of lenses, such as a zoom lens system or a single focal length lens system, a portion of the incident light is reflected at an inner surface of an outer circumferential part of each lens. Therefore, the reflected light, which is undesired light, might be cast into the range of an aperture for photographing. If such undesired light reaches an imaging surface, noise such as flare or ghost occurs, and thereby image characteristics are deteriorated.
In order to suppress occurrence of such undesired light that causes noise such as flare or ghost, various kinds of lenses each having an outer circumferential part subjected to black coating have conventionally been proposed.
Japanese Laid-Open Patent Publication No. 11-337707 discloses a lens in which a cut plane as an edge plane of an outer peripheral part is entirely coated with a black non-transmitting coating serving as means for preventing reflection of a harmful light beam.
Japanese Laid-Open Patent Publication No. 2008-129133 discloses an image forming lens for use in an image pickup module, in which a portion of an outer peripheral part of a flange, on which a taper is formed, is coated with an adhesive agent containing a black coating material.
Japanese Patent Publication No. 61-043688 discloses a reflection objective lens having an annular part entirely coated with a black coating material.
Japanese Laid-Open Patent Publication No. 11-326604 discloses a lens in which a taper is formed on a side surface, and each rough surface on an incident surface side where the taper is formed is entirely black coated.
Further, as a lens constituting the imaging optical system, a lightweight and relatively inexpensive plastic lens has been widely used. Also in the case of using such a plastic lens, occurrence of undesired light that causes noise such as flare or ghost needs to be suppressed.
In the case of a lens made of a glass material, a coating material for coloring the lens in black is usually less viscous, and therefore, can be relatively easily applied to a target surface. Accordingly, uneven coating, such as excess/shortage of a coating range or an uneven thickness of a coating layer, is less likely to occur, decentering error is not increased so much, and dimensional accuracy of the lens diameter is not lowered so much.
However, in the case of a plastic lens, a coating material for coloring the plastic lens in black is usually highly viscous, and particularly the thickness of a coating layer is likely to be increased more than necessary, which might cause uneven coating. Accordingly, in order to suppress an increase in decentering error and maintain the dimensional accuracy of the lens diameter, a target surface to be coated should be limited to a portion of a side surface of the lens. Further, if such a highly viscous coating material is applied to a portion of the side surface where a taper is formed, the thickness of the coating layer becomes uneven and the coating range is excessively increased. Accordingly, it is very difficult to suppress an increase in decentering error, and maintain the dimensional accuracy of the lens diameter.